1. Field of the Invention
The present invention relates to a cylinder-bed type sewing machine which is preferably used for stitching tubular sewing products such as cuffs of trousers, or sleeve edges of a T-shirt, and more particularly to an improved driving mechanism for a feed dog which allows a work support unit to be formed into a cylindrical shape so that a tubular sewing product is sewn while being fitted onto the work support cylinder unit, and the tubular sewing product to be fed rearward along the outer periphery of the work support cylinder unit.
2. Description of the Prior Art
Conventionally, such a sewing machine is disclosed in, for example, Laid Open Japanese Patent Application Nos. 62-240,093 and 4-20,372. The disclosed sewing machines are provided with a work support unit which is formed into a substantially rectangular box-like shape. A throat plate is disposed on the upper face of the substantially rectangular box-like work support unit, and a feed dog is disposed so that a sewing product on the throat plate is fed rearward in synchronization with the vertical motion of a sewing needle. The feed dog is configured so as to circulate along a locus which is substantially rectangular.
In such a prior art sewing machine, a tubular sewing product is usually fitted onto the work support unit to be held thereon and then subjected to the sewing operation. In such a prior art example in which the work support unit is formed into a substantially rectangular box-like shape, the work support unit has a large peripheral length. When a sewing product having a small peripheral length, such as a sleeve edge of children's wear is to be sewn, therefore, it is impossible to fit the sewing product onto the work support unit to be held thereon. Consequently, the kinds of sewing products which can be sewn by the sewing machine are restricted, and hence the sewing machine has a drawback of reduced versatility.
Although not shown, another prior art sewing machine has been proposed in which a work support unit is formed into a cylindrical shape so that the distance between the left end of the cylindrical work support unit and a throat plate is reduced as much as possible. The sewing machine cannot be used for a tubular sewing product which must be sewn while being fitted deeply onto the work support unit, thereby giving rise to a problem of applicability. Also in a cylinder-bed type sewing machine in which a cylinder of the work support has a small peripheral length so as to cope with a tubular sewing product of a small peripheral length, when a feed dog is configured so as to circulate along a locus which is substantially rectangular in the same manner as the feed dog of the above-described prior art example, the feed dog conducts the feeding operation on the sewing product while making point contact with the sewing product, and therefore the sewing product cannot be fed properly and smoothly.